1. Field of the Invention
This invention relates to a drilling fluid circulation system, and more particularly to a closed loop circulation system including a separator for handling drilling fluid and its associated drilling cuttings and produced gas.
2. The Prior Art
Much of the drilling fluid technology was developed by the oil and gas industry. Typically, a drilling mud is pumped down a drill string in a well being drilled from the surface, circulated back up the outside of the drill string to an open tank or reservoir at the surface, and recirculated down the drill string. Usually the return discharge empties into an open screen or other cuttings-removal device.
Horizontal drilling in coal mines has been investigated recently as a technique for degasification of a coal seam in advance of mining. Drilling of one or more boreholes a distance of 300 meters or more into a coal seam and recovering methane therefrom significantly reduces the methane concentration in the working area of a mine during later mining of the seam.
One of the problems encountered in horizontal drilling through a coal seam is that the working area is relatively small and enclosed, such that gas produced from the borehole being drilled, if released into the working area, presents a significant hazard. Prior art attempts to solve this problem have employed a liquid seal in the drilling fluid circulation system that forms a barrier between the mine atmosphere and the gas discharge point. However, because of surges in the gas flow this type of liquid seal was often blown out or made ineffective due to being plugged by drill cuttings.
The present invention overcomes these problems by providing a closed loop system for containing drill cuttings, gas and clean drilling fluid in a way to ensure safe and efficient separation. The closed system is desirable to prevent spillage of the drilling fluid and release in the working area of the gas produced while drilling.